Ion storage, ion separation, and ion detection are the principal functions of conventional mass spectrometers, which are generally housed in different components. As a consequence, interfaces that are typically complicated are often used between the components, rendering more difficult, firstly, a compact and efficient solution and, secondly, a quick manipulation of the ion populations. Moreover, there are signal losses, which reduces power and sensitivity of mass spectrometers, associated with the transfer of ions through the interfaces. By contrast, many functions (e.g. ion production, ion storage, and ion detection) can be unified “in situ” in the same ion trap and very compactly in the case of an electric or, optionally, magnetic Fourier transform ion trap (abbreviated: FT ion trap).
Ions or ionized gas constituents can be measured in a non-reactive manner and without interruption, and can be verified or detected according to their mass-to-charge ratio in such an FT iron trap, as described in e.g. the article: “A novel electric ion resonance cell design with high signal-to-noise ratio and low distortion for Fourier transform mass spectrometry”, by M. Aliman and A. Glasmachers, Journal of The American Society for Mass Spectrometry; Vol. 10, No. 10, October 1999.
An example of a mass spectrometer with an electric FT ion trap is described in DE 10 2013 208 959 A. The FT ion trap has a ring electrode and two further electrodes (cap electrodes). The ions stored in the FT ion trap are excited in situ and the detection of the excited ions is effectuated by recording and evaluating mirror charges which the stored ions induce on the cap electrodes of the FT ion trap. In order to measure mirror charges, the ions stored in the FT ion trap are excited (stimulated) in a broadband fashion in situ and the ions oscillate at characteristic resonance frequencies in the ion trap, depending on the mass-charge ratio. This procedure differs fundamentally from the conventional destructive detection methods, in which the ions are no longer available after the measurement.
WO 2015/003819 A1 discloses the practice of removing individual ion populations from the ion trap or suppressing the ion populations if the particle number thereof exceeds a predetermined threshold at a given mass-to-charge ratio in an FT-ICR (“Fourier transform ion cyclotron resonance”) trap by way of an IFT excitation in the form of a so-called SWIFT (“storage wave-form inverse Fourier transform”) excitation. In this way, it is possible to remove large ion populations from the ion trap such that certain subsets of ion populations can be measured more accurately.